The present invention relates to a device and to a corresponding method for separating one or a plurality of material fractions from at least one material stream of free-flowing bulk material.
Such a method and a corresponding device, respectively, are used inter alia for sorting material mixtures, in particular of plastics materials, for the purpose of recycling. The material mixture to be sorted herein is composed of recycling material such as beverage bottles, foodstuff packaging, or other plastics-material items, for example from old electronic appliances or from automobile recycling, that has been comminuted to fragments. The individual fragments that are contained in the material mixture herein have to be sorted according to the type of plastics material and optionally according to other properties such as color, degree of contamination, or similar, so as to harvest therefrom homogeneous and recyclable material fractions.
Hereby, a material stream of the material mixture to be sorted is optically scanned and subjected to spectroscopic identification. The individual fragments that are contained in the material stream by means of their material properties thus detected are then mechanically separated in that said fragments are selectively deflected to different selection channels.
A method and a corresponding device for separating plastics materials, in which a material stream of the plastics materials that are comminuted to fragments is conveyed on a transportation belt, are known from publication DE 198 16 881. The material stream herein is scanned line-by-line perpendicularly to the transportation direction by way of a laser beam, and the optical radiation that is remitted by the fragments is spectroscopically analyzed. The individual fragments by virtue of the identification results are classified into different groups, and are separated into separate fractions by a separation system, for example by way of synchronized nozzles.
Publication DE 101 49 505 discloses a sorting apparatus for plastics materials, in which a material stream from plastics-material fragments under the influence of gravity is guided across an incline. The material stream on its way along the incline is analyzed by way of an optical spectrometer, and the individual fragments are separated into at least two material fractions at the end of the incline by way of a separation unit that is operated with nozzle jets.
A disadvantage of the sorting installations known in the prior art lies in that only a relatively low material throughput can be achieved with the former. In this way, the belt speed cannot be arbitrarily increased in the case of a sorting installation having a mechanical transportation belt, or a higher belt speed leads to increased belt wear, respectively, on the one hand. In the case of an incline being used, the mutual overlap of the fragments which would lead to a poor or erroneous sorting result, respectively, limits the mass stream which can be infed to the incline. The mass throughput is thus limited by the geometric dimensions of the incline. Moreover, the variable spacing between the scanner and the fragment in the case of optical scanning of the fragments leads to a “tangent error” during scanning.
In order for the large mass streams that are required for an economical operation in the case of an application for recycling plastics materials from old electronic appliances or automobiles, for example, to be managed, an object of the invention lies in providing a device and a method of the type mentioned at the outset by way of which a higher material throughput or a higher sorting speed, respectively, may be achieved.